So-called instantaneous water heaters are known. These heaters generally provide for rapid heating of water as it flows through the heater and are in contrast to other types of heaters that heat water at a relatively slow rate and provide storage for heated water. Instantaneous water heater can be either "open" or "closed." An open system is placed at the outlet of a water line and services a single outlet, while a closed system is placed in a water line that includes a plurality of separately controlled outlet valves.
U.S. Pat. No. 4,638,147 (Dytch et al.) shows, for example, an open flow-through heater that includes a plurality of heating elements in a single chamber, the elements being switched on to effect a predetermined heating. The flow rate is measured by a turbine, and the output of the heating elements is determined by a microprocessor that, in turn, controls a number of triacs connected to the heating elements.
U.S. Pat. No. 4,604,515 (Davidson) shows another water heater wherein a chamber has a plurality of baffles for creating a serpentine flow path. U.S. Pat. No. 4,410,791 (Eastep) discloses an instantaneous water heater having a heating element comprised of a plurality of heating plates molded into the water heater core. A number of tapered ceramic projections extend into the flow path and between the heating plates to provide a serpentine flow over the plates. U.S. Pat. No. 4,713,525 (Eastep) teaches an improved control for the '791 patent.
Other instantaneous water heater systems are shown in U.S. Pat. Nos. 4,808,793 (Hurko), 5,020,127 (Eddas), and 5,129,034 (Syndenstricker).